Phenol, from benzene oxidation

Examples for necessary process improvements through catalyst research are the development of one-step processes for a number of bulk products like acetaldehyde and acetic acid (from ethane), phenol (from benzene), acrolein (from propane), or allyl alcohol (from acrolein). For example, allyl alcohol, a chemical which is used in the production of plasticizers, flame resistors and fungicides, can be manufactured via gas-phase acetoxylation of propene in the Hoechst [1] or Bayer process [2], isomerization of propene oxide (BASF-Wyandotte), or by technologies involving the alkaline hydrolysis of allyl chloride (Dow and Shell) thereby producing stoichiometric amounts of unavoidable by-products. However, if there is a catalyst... 

A specificity of N20 oxidant compared to 02 is one of the most interesting points arising from benzene oxidation over FeZSM-5 zeolites. The specificity is clearly seen from the results presented in Table 7.6 [ 118]. With nitrous oxide, benzene conversion is 27% at 623 K, whereas with dioxygen it is only 0.3% at 773 K. Moreover, the reaction route changes totally N20 leads to selective formation of phenol, while 02 leads only to the products of complete oxidation. 

The aim of the project was to investigate different gas-phase reactions. In particular, alternative routes for the synthesis of propylene oxide [101,102] and the synthesis of phenol from benzene and N20 [103] should be found. As a first milestone a throughput of approximately 15-20 molProduct kgCat 1 h 1 was targeted. 

The one-step hydroxylation ofbenzene represents an attractive alternative pathway for the direct synthesis of phenol and many studies are performed using different processes among which the photocatalytic reaction [45,46]. One of the main problem is the low selectivity of the process due to the higher reactivity of phenol towards the oxidation than benzene with the formation of oxidation by-products. In order to avoid these secondary products and to obtain the separation of the phenol from the oxidant reaction environment the use of a membrane system coupled with the photocatalytic process seems a useful solution. 

Although significant improvements have been made in the synthesis of phenol from benzene, the practical utility of direct radical hydroxylation of substituted arenes remains very low. A mixture of ortho-, meta- and para-substituted phenols is typically formed. Alkyl substituents are subject to radical H-atom abstraction, giving benzyl alcohol, benzaldehyde, and benzoic acid in addition to the mixture of cresols. Hydroxylation of phenylacetic acid leads to decarboxylation and gives benzyl alcohol along with phenolic products [2], A mixture of naphthols is produced in radical oxidations of naphthalene, in addition to diols and hydroxyketones [19]. 

Yields of phenol from the oxidation of benzene by hydrogen peroxide and... 

With worldwide phenol consumption exceeding 5 million tons in 1995, optimizing production routes of this essential chemical becomes very important. As an alternative to the traditional cumene process, a one-step-synthesis of phenol from benzene is highly desirable. With a ZSM5 type zeolite in its acid form as catalyst and nitrous oxide as oxidant, benzene may be directly oxidized to phenol [1-4] ... 

The catalytic effect of the nitric acid gas has been attributed to (a) increase in the concentration of active oxygen and (b) greater oxidizing power of nitrogen peroxide.27 The formation of phenol from benzene by electrochemical oxidation has been explained on the basis of atomic oxygen,18 a hypothesis that may hold in this case. A mechanism for the catalytic effect of nitrogen peroxide based on the conclusion that it is readily activated by the absorption of radiation over a relatively wide range of frequencies is as follows ... 

These processes perform the oxidation of hydrochloric add in situ. Their principle is similar to the one implemented to produce phenol from benzene by the Hooker/Raschig process (see Section 10.1.3). The first industrial ethylene oxychlorination plant was built by Dow in the United States in 1955. 

The reaction of oxepin (228 R = H) was complicated by the simultaneous photochemical reaction of benzene oxide, the valence isomer of oxepin.26 The results varied with solvent, temperature, and wavelength.269 The reaction proceeded with high selectivity to 2-oxa-bicyclo[3.2.0]hepta-3,6-diene (229 R = H) upon irradiation (A >310 nm) at room temperature. In most other cases the reaction was attended with the formation of phenol, probably from benzene oxide via Dewar benzene oxide, as this compound is known to isomerize photo-... 

Analogously, in the presence of silica-supported palladium catalysts, benzene is oxidized under ambient conditions to give phenol, benzoquinone, hydroquinone and catechol [37b]. Palladium chloride, used for the catalyst preparation, is believed to be converted into metallic palladium. The synthesis of phenol from benzene and molecular oxygen via direct activation of a C-H bond by the catalytic system Pd(OAc)2-phenanthroline in the presence of carbon monoxide has been described [38]. The proposed mechanism includes the electrophilic attack of benzene by an active palladium-containing species to to produce a a-phenyl complex of palladium(ll). Subsequent activation of dioxygen by the Pd-phen-CO complex to form a Pd-OPh complex and its reaction with acetic acid yields phenol. The oxidation of propenoidic phenols by molecular oxygen is catalyzed by [A,A"-bis(salicylidene)ethane-l,2-diaminato]cobalt(ll)[Co(salen)] [39]. 

Boron, Phosphorus, and Selenium Compounds. Oxone has been used to oxidize carbon-boron bonds during the work-up of hydroboration reactions to obtain high yields of the resultant alcohols (eq 73). Aqueous Oxone/acetone oxidizes electron-poor and electron-rich aromatic and aliphatic boronic acids and esters to the corresponding alcohols rapidly and efficiently (eq 74). A one-pot procedure for the synthesis of iweta-substituted phenols from benzenes has been developed, and a similar strategy has been devised for the synthesis of Boc-oxindoles from Boc-indoles. i3i... 

The hydroxylation of the aromatic nucleus by hydroxyl radicals, generated by decomposition of hydrogen peroxide in the presence of iron(II) ions, may be applied to the electrochemical synthesis of phenol from benzene, since the concentration of the iron(II) ions can be controlled by the cathodic reduction of iron(ni) ions formed by oxidation of iron(II) ions wiA H2O2. 

A very important application of zeolites includes in the hydration/dehy-dration reactions. A very interesting example is the Asahi process for the hydration of cyclohexene to cyclohexanol over a high silica (Si/Al>20), H-ZSM-5 type catalyst [44]. The process has been operated successfully on a 60,000 tons per year since 1990. However, this process has a problem of catalyst deactivation. The hydration of cyclohexanene is a key step in an alternative route to cyclohexanone (and phenol) from benzene (Figure 11.11). The conventional route involves hydrogenation of cyclohexane followed by auto-oxidation to a mixture of cyclohexanol and cyclohexanone and subsequent dehydrogenation of the former. A disadvantage of this process is only 75-80% selectivity at very low conversions (ca. 5%), thus one has to the recycle of enormous quantities of cyclohexane. 

Solutia (USA), in joint work with the Boreskov Institute of Catalysis, Russia, developed a one-step process to manufacture phenol from benzene using nitrous oxide as the oxidant (see Fig. 3.12). Nitrous oxide (a greenhouse gas) is a waste product from Solutia s adipic acid process. The preferred catalysts are acidified ZSM-5 and ZSM-11 zeolites containing iron or a silica/alumina ratio of 100 1 containing 0.45 wt% iron(III) oxide. The catalyst s half-life is 3 to 4 days, and it can be restored by passing air through the bed at high temperatures. 

Oxidation with Molecular Oxygen Molecular oxygen is the most attractive oxidant from both economic and environmental viewpoints [8-10]. The direct synthesis of phenol from benzene using is one of the most difficult challenges for catalysis [58]. 

The formation of phenol from benzene using N2O as the oxidant on various metal oxides was demonstrated in the early 1980s. The phenol obtained from benzene oxidation, which is incorporated in the adipic acid production process, can be hydrogenated to cyclohexanone. The nitric acid oxidation of cyclohexanol and cyclohexanone forms N2O which can he recycled, thus closing the N2O cycle. ... 

Acetoxybenzene is prepared by the reaction of benzene with Pd(OAc)2[325,342-345], This reaction is regarded as a potentially useful method for phenol production from benzene, if carried out with only a catalytic amount of Pd(OAc)2. Extensive studies have been carried out on this reaction in order to achieve a high catalytic turnover. In addition to oxygen and Cu(II) salts, other oxidants, such as HNOi, nitrate[346,347], potassium peroxodisulfate[348], and heteropoly acids[349,3S0], are used. HNO is said to... 

Starting from Benzene. In the direct oxidation of benzene [71-43-2] to phenol, formation of hydroquinone and catechol is observed (64). Ways to favor the formation of dihydroxybenzenes have been explored, hence CuCl in aqueous sulfuric acid medium catalyzes the hydroxylation of benzene to phenol (24%) and hydroquinone (8%) (65). The same effect can also be observed with Cu(II)—Cu(0) as a catalytic system (66). Efforts are now directed toward the use of Pd° on a support and Cu in aqueous acid and in the presence of a reducing agent such as CO, H2, or ethylene (67). Aromatic... 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Direct hydroxylation of benzene to phenol could be achieved using zeolite catalysts containing rhodium, platinum, palladium, or irridium. The oxidizing agent is nitrous oxide, which is unavoidable a byproduct from the oxidation of KA oil (see KA oil, this chapter) to adipic acid using nitric acid as the oxidant. 

Thermolysis (115°C) or irradiation of the epoxide 3, generated from bicyclo[2.2.0]hexa-2,5-diene ( Dewar benzene") with 3-chloroperoxybenzoic acid, gives a mixture of the valence tautomers oxcpin and benzene oxide together with traces of phenol.111112... 

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